The invention disclosed herein relates generally to motion converting mechanisms, and more particularly to transducer mounting means for varying the vertical and horizontal directions of a transducer in response to motions of control shaft means.
Mechanisms for remotely producing rotation of an object about two mutually perpendicular axes are required in a number of varied applications. One such application is in the echo sounding field in which it is necessary to control the beam direction of an electroacoustic transducer typically located underwater, outside the hull of a marine vessel from a control station located inside the vessel. Echo sounding apparatus of this type is frequently designed such that the transducer and stem on which it is mounted can be retracted into the vessel. Since it is important that any perforations of the vessel hull be kept as small as feasible, transducer apparatus of the type described above should be compact.
In many common echo sounding transducer applications the transducer must be rotatable throughout 360.degree. in a horizontal plane, and tiltable throughout a significant vertical range. Further, it is important that the transucer maintain any direction to which it is set. Achieving this requirement is complicated by the fact that a marine vessel does not provide a stable platform for fixed mounting of the transducer.
Oscillation of the vessel about an axis parallel with the beam axis of the transducer has only a relatively minor effect on transducer beam direction. However, oscillation of the vessel about an axis perpendicular to the transducer beam axis has a substantial effect on beam direction, and must be compensated for. It is, of course, possible to continuously sense vessel orientation relative to some fixed reference and to continuously reposition the transducer relative to the vessel to compensate for vessel movement. Such a compensation system is relatively complex and expensive, and desirably should be avoided.
A simpler approach is to pendulously suspend the transducer from the vessel at least about an axis parallel with the tilt axis of the transducer. Where a pendulous transducer mounting is used and transducer direction is controlled by rotatable shaft means, it is necessary to provide for transmitting vertical and horizontal transducer control motions across a joint which allows relative movement between the transducer and vessel. For obvious reasons, it is desirable to keep the transducer mount and directional control mechanism as simple as possible.
A variety of mechanisms for achieving rotation of an electroacoustic transducer about two orthogonal axes are known. For example, German Pat. No. 28 03 617 discloses echo sounding apparatus having an electroacoustic transducer tiltably mounted about a horizontal tilt axis in a pendulously suspended frame.
The mechanism for varying the direction of the transducer in horizontal and vertical planes comprises a pair of concentric vertical control shafts. The frame is carried on one of the shafts so as to be rotatable with that shaft about a vertical axis. Tilt of the transducer is achieved by means of a pinion coupled to the other control shaft. The pinion meshes with a gear segment fixed to the back of the transducer so that rotation of the shaft causes rotation of the transducer about the tilt axis.
Such an arrangement is satisfactory for rotating the transducer about mutually perpendicular axes. However, it requires a special pinion gear and mating gear segment. Such a gear arrangement is not uncommon, but does require gears which are inherently more difficult to form than other simpler mechanism.
More importantly, the gear arrangement must occupy a location centered behind the transducer and located generally above and/or behind the transducer tilt axis. Accordingly, as the transducer tilts, it swings in an arc, and thus requires somewhat more space for tilting purposes than if it were centered on the tilt axis. The transducer assembly also generally tends to be unbalanced about the tilt axis because the center of gravity of transducer is generally offset from directly below the tilt axis. This unbalance varies with the tilt direction of the transducer. It also requires maintaining of a positioning torque on the tilt control shaft, which, in turn, must be opposed by a counter torque on the horizontal position control shaft in order to maintain a desired transducer beam direction.
Other mechanical arrangements for remotely achieving rotation about two orthogonal axis are shown in U.S. Pat. Nos. 2,829,360, 2,881,408 and 3,454,923 respectively issued to R. Allyn on Apr. 1, 1958, J. Dudley on Apr. 7, 1959 and W. Currie on July 8, 1969. The mechanisms disclosed in each of these patents includes a single control shaft which is rotatable about and translatable along a vertical axis. Rotation of the control shaft causes rotation of the transducer in a horizontal plane. Translation or linear motion of the control shaft controls tilt of the transducer in a vertical plane. The mechanisms shown in the first two of these patents suffer from unbalance of the transducer about the tilt axis in a manner similar to that described for the mechanism of German Pat. No. 28 03 617, although they do avoid unbalance induced coupling between motions about the horizontal and vertical axes.
The mechanism disclosed in the third patent avoids unbalance of the transducer assembly by centering the transducer on the tilt axis and fitting a pinion on the end of a shaft which extends along the tilt axis. The pinion meshes with a rack gear, and is vertically movable relative thereto in response to linear motion of the control shaft so as to rotate the transducer about the tilt axis. Pendulous mounting is not provided by any of the mechanisms shown in the U.S. patents. Also, these mechanisms require some means for counteracting the effects of weight of the control shaft.
The applicant has devised a unique mechanism for controlling the rotation of a pendulously suspended transducer about horizontal and vertical axes which avoids the above noted disadvantage of prior art mechanisms. Specifically, the mechanism is compact so as to require minimum space for rotation about horizontal and vertical axes. It is inherently simple and inexpensive to manufacture, in that it does not utilize gear arrangements. Finally, the transducer is supported in a balanced manner so as to avoid problems resulting from torques which tend to cause the transducer deviate from its desired orientation.